Our principle aim has been to understand the molecular mechanisms by which electron transport chains are able to act as proton pumps. It is now generally accepted that the processes through which the energy of light or oxidative metabolism are conserved involve proton circuits in which the electron transfer chains provide the principle driving force for the proton current. It is clear that the fundamental mechanisms involved are essentially the same photosynthesis and respiration. The photosynthetic bacteria is the best system available for studying the kinetics of these processes, and such studies provided information essential to understanding of the less accessible respiratory systems. Our objectives have been (1) the further characterization of the components of the electron transfer chains; (2) detailed kinetic studies to identify reaction pathways; (3) studies using systems modified by mutation inhibition or extraction to identify the role of specific components; (4) a reassessment of the relative stoichiometries of components; (5) measurement of kinetic stoichiometric and thermodynamic parameters of the proton gradient; (6) the development of techniques and instrumentaion to facilitate these measurements.